MOSCOW, July 27, 2014 (AFP) - The 29-year-old who led from day one looked to have thrown away his overnight lead when he double bogeyed the 12th and dropped another shot at 14. McGrane shot a final round six under par 66 to take the clubhouse lead.
However Horsey chipped in a remarkable eagle at 17 before scrambling par at the last to finish level with McGrane on 17 under at the Tseleevo Golf and Polo Club outside Moscow.
The two men settled the affair at the first playoff hole when Horsey two putted for par and McGrane bogeyed the hole after finding a greenside bunker with his approach.
"I'm relieved really - that's the word that sums it up and it was quite similar to my last win, in Morocco, where I made a bit of a mess of a couple of holes on the back nine," said Horsey.
"I didn't know where I was in the tournament until the 17th when I hit it through the back of the green there and then realised I was three behind and needed to do something drastic quite quickly.
"I managed to chip in there and was trying to make birdie at the last. I didn't realise Damien had dropped one (bogey at 18), but I managed to get up and down there and was fortunate to win the play-off as well." he added.
Scotland's Scott Jamieson took third spot after a solid three under par 69 while Englishman Sam Hutsby, was a further shot back in fourth after carding a 68.
Peter Whiteford of Scotland, who shared the overnight lead with Horsey, slumped to a three over 75 and a fifth place finish.
It was Horsey's first win in 89 EPGA events and could lift him from his current ranking of 198 in the world to inside the top 120.
"I knew the chip on 17 had to go in. I knew by that point that I was three behind so I needed it to go in. This is a very special win. It's been a while and it's been a bit of a bumpy road
McGrane's defeat meant he missed out on a chance for his second EPGA victory after the China Open in 2008.
"I played lovely all week so I'm very pleased with my week. I'm a little disappointed not to do better in the play-off there, but I've hit good shots all week and putted reasonably well.
"There are a lot of good events before the end of the year and this has given me a lot of confidence going into them," said the 43-year-old from County Meath.
Leading scores after the fourth and final round of the EPGA Russian Open on Sunday (par 72):
275 - David Horsey (ENG) 65 68 70 72, Damien McGrane (IRL) 69 71 69 66
* Horsey won at first play-off hole
276 - Scott Jamieson (SCO) 66 72 69 69
277 - Sam Hutsby (ENG) 72 67 70 68
278 - Peter Whiteford (SCO) 66 71 66 75
279 - Krister Eriksson (SWE) 72 68 71 68, Thomas Pieters (BEL) 67 68 72 72
280 - Maximilian Kieffer (GER) 67 71 73 69, Andrea Pavan (ITA) 73 70 64 73
281 - Sam Walker (ENG) 69 71 73 68, Carlos Del Moral (ESP) 70 71 73 67
282 - Adrien Saddier (FRA) 69 73 70 70, Mikko Korhonen (FIN) 74 71 68 69, Brinson Paolini (USA) 72 71 70 69, Fredrik Andersson Hed (SWE) 70 69 77 66, Haydn Porteous (RSA) 72 71 70 69, Dean Huizing (NED) 72 74 69 67
283 - Gary Boyd (ENG) 69 68 72 74, James Heath (ENG) 71 72 71 69, Jorge Campillo (ESP) 68 76 68 71, Seuk-hyun Baek (KOR) 74 70 69 70, Alastair Forsyth (SCO) 75 70 70 68, JB Hansen (DEN) 69 73 71 70
284 - Jamie McLeary (SCO) 68 72 70 74, Soren Hansen (DEN) 72 69 69 74
285 - Nacho Elvira (ESP) 69 69 77 70, Gaganjeet Bhullar (IND) 67 71 75 72, Stuart Manley (WAL) 71 73 71 70, Andreas Harto (DEN) 73 70 73 69, Adam Gee (ENG) 70 75 69 71, Oliver Bekker (RSA) 67 76 72 70, Javier Colomo (ESP) 72 68 71 74